12-Bit, 8-Channel Sampling ANALOG-TO-DIGITAL CONVERTER with I 2 C Interface

Transcription

1 ADS7828 ADS7828 NOVEMBER REVISED MARCH Bit, 8-Channel Sampling ANALOG-TO-DIGITAL CONVERTER with I 2 C Interface FEATURES 8-CHANNEL MULTIPLEXER 50kHz SAMPLING RATE NO MISSING CODES 2.7V TO 5V OPERATION INTERNAL 2.5V REFERENCE I 2 C INTERFACE SUPPORTS: Standard, Fast, and High-Speed Modes TSSOP-16 PACKAGE APPLICATIONS VOLTAGE-SUPPLY MONITORING ISOLATED DATA ACQUISITION TRANSDUCER INTERFACES BATTERY-OPERATED SYSTEMS REMOTE DATA ACQUISITION DESCRIPTION The ADS7828 is a single-supply, low-power, 12-bit data acquisition device that features a serial I 2 C interface and an 8-channel multiplexer. The Analog-to-Digital (A/D) converter features a sample-and-hold amplifier and internal, asynchronous clock. The combination of an I 2 C serial, 2-wire interface and micropower consumption makes the ADS7828 ideal for applications requiring the A/D converter to be close to the input source in remote locations and for applications requiring isolation. The ADS7828 is available in a TSSOP-16 package. CH0 CH1 SAR CH2 CH3 CH4 CH5 CH6 CH7 COM 8-Channel MUX S/H Amp CDAC Comparator Serial Interface SDA SCL A0 A1 REF IN /REF OUT Buffer 2.5V V REF Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. I 2 C is a trademark of Koninklijke Philps Electronics N.V. All other trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright , Texas Instruments Incorporated

2 ABSOLUTE MAXIMUM RATINGS (1) +V DD to GND V to +6V Digital Input Voltage to GND V to +V DD + 0.3V Operating Temperature Range C to +105 C Storage Temperature Range C to +150 C Junction Temperature (T J max) C TSSOP Package Power Dissipation... (T J max T A )/θ JA θ JA Thermal Impedance C/W Lead Temperature, Soldering Vapor Phase (60s) C Infrared (15s) C NOTE: (1) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION (1) MAXIMUM INTEGRAL SPECIFIED LINEARITY PACKAGE TEMPERATURE ORDERING TRANSPORT PRODUCT ERROR (LSB) PACKAGE-LEAD DESIGNATOR RANGE NUMBER MEDIA, QUANTITY ADS7828E ±2 TSSOP-16 PW 40 C to +85 C ADS7828E/250 Tape and Reel, 250 " " " " " ADS7828E/2K5 Tape and Reel, 2500 ADS7828EB ±1 TSSOP-16 PW 40 C to +85 C ADS7828EB/250 Tape and Reel, 250 " " " " " ADS7828EB/2K5 Tape and Reel, 2500 NOTE: (1) For the most current package and ordering information, see the Package Option Addendum at the end of this data sheet, or see the TI web site at. PIN CONFIGURATION PIN DESCRIPTIONS Top View CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH ADS TSSOP +V DD SDA SCL A1 A0 COM REF IN / REF OUT GND PIN NAME DESCRIPTION 1 CH0 Analog Input Channel 0 2 CH1 Analog Input Channel 1 3 CH2 Analog Input Channel 2 4 CH3 Analog Input Channel 3 5 CH4 Analog Input Channel 4 6 CH5 Analog Input Channel 5 7 CH6 Analog Input Channel 6 8 CH7 Analog Input Channel 7 9 GND Analog Ground 10 REF IN / REF OUT Internal +2.5V Reference, External Reference Input 11 COM Common to Analog Input Channel 12 A0 Slave Address Bit 0 13 A1 Slave Address Bit 1 14 SCL Serial Clock 15 SDA Serial Data 16 +V DD Power Supply, 3.3V Nominal 2 ADS7828

3 ELECTRICAL CHARACTERISTICS: +2.7V At T A = 40 C to +85 C, +V DD = +2.7V, V REF = +2.5V, SCL Clock Frequency = 3.4MHz (High-Speed Mode), unless otherwise noted. ADS7828E ADS7828EB PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS ANALOG INPUT Full-Scale Input Scan Positive Input - Negative Input 0 V REF 0 V REF V Absolute Input Range Positive Input 0.2 +V DD V DD V Negative Input V Capacitance pf Leakage Current ±1 ±1 µa SYSTEM PERFORMANCE No Missing Codes Bits Integral Linearity Error ±1.0 ±2 ±0.5 ±1 LSB (1) Differential Linearity Error ±1.0 ±0.5 1, +2 LSB Offset Error ±1.0 ±3 ±0.75 ±2 LSB Offset Error Match ±0.2 ±1 ±0.2 ±1 LSB Gain Error ±1.0 ±4 ±0.75 ±3 LSB Gain Error Match ±0.2 ±1 ±0.2 ±1 LSB Noise µvrms Power-Supply Rejection db SAMPLING DYNAMICS Throughput Frequency High Speed Mode: SCL = 3.4MHz khz Fast Mode: SCL = 400kHz 8 8 Standard Mode, SCL = 100kHz 2 2 khz Conversion Time 6 6 µs AC ACCURACY Total Harmonic Distortion V IN = 2.5V PP at 10kHz db (2) Signal-to-Ratio V IN = 2.5V PP at 10kHz db Signal-to-(Noise+Distortion) Ratio V IN = 2.5V PP at 10kHz db Spurious-Free Dynamic Range V IN = 2.5V PP at 10kHz db Isolation Channel-to-Channel db VOLTAGE REFERENCE OUTPUT Range V Internal Reference Drift ppm/ C Output Impedance Internal Reference ON Ω Internal Reference OFF 1 1 GΩ Quiescent Current Int. Ref. ON, SCL and SDA pulled HIGH µa VOLTAGE REFERENCE INPUT Range 0.05 V DD 0.05 V DD V Resistance 1 1 GΩ Current Drain High Speed Mode: SCL= 3.4MHz µa DIGITAL INPUT/OUTPUT Logic Family CMOS CMOS Logic Levels: V IH +V DD 0.7 +V DD V DD 0.7 +V DD V V IL 0.3 +V DD V DD 0.3 V V OL Min. 3mA Sink Current V Input Leakage: I IH V IH = +V DD µa I IL V IL = µa Data Format Straight Straight Binary Binary ADS7828 HARDWARE ADDRESS Binary POWER-SUPPLY REQUIREMENTS Power-Supply Voltage, +V DD Specified Performance V Quiescent Current High Speed Mode: SCL = 3.4MHz µa Fast Mode: SCL = 400kHz µa Standard Mode, SCL = 100kHz µa Power Dissipation High Speed Mode: SCL = 3.4MHz µw Fast Mode: SCL = 400kHz µw Standard Mode, SCL = 100kHz µw Power-Down Mode High Speed Mode: SCL = 3.4MHz µa w/wrong Address Selected Fast Mode: SCL = 400kHz µa Standard Mode, SCL = 100kHz 6 6 µa Full Power-Down SCL Pulled HIGH, SDA Pulled HIGH na TEMPERATURE RANGE Specified Performance C NOTES: (1) LSB means Least Significant Bit. With V REF equal to 2.5V, 1LSB is 610µV. (2) THD measured out to the 9th-harmonic. ADS7828 3

4 ELECTRICAL CHARACTERISTICS: +5V At T A = 40 C to +85 C, +V DD = +5.0V, V REF = External +5.0V, SCL Clock Frequency = 3.4MHz (High-Speed Mode), unless otherwise noted. ADS7828E ADS7828EB PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS ANALOG INPUT Full-Scale Input Scan Positive Input - Negative Input 0 V REF 0 V REF V Absolute Input Range Positive Input 0.2 +V DD V DD V Negative Input V Capacitance pf Leakage Current ±1 ±1 µa SYSTEM PERFORMANCE No Missing Codes Bits Integral Linearity Error ±1.0 ±2 ±0.5 ±1 LSB (1) Differential Linearity Error ±1.0 ±0.5 1, +2 LSB Offset Error ±1.0 ±3 ±0.75 ±2 LSB Offset Error Match ±1 ±1 LSB Gain Error ±1.0 ±3 ±0.75 ±2 LSB Gain Error Match ±1 ±1 LSB Noise µvrms Power-Supply Rejection db SAMPLING DYNAMICS Throughput Frequency High Speed Mode: SCL = 3.4MHz khz Fast Mode: SCL = 400kHz 8 8 khz Standard Mode, SCL = 100kHz 2 2 khz Conversion Time 6 6 µs AC ACCURACY Total Harmonic Distortion V IN = 2.5V PP at 10kHz db (2) Signal-to-Ratio V IN = 2.5V PP at 10kHz db Signal-to-(Noise+Distortion) Ratio V IN = 2.5V PP at 10kHz db Spurious-Free Dynamic Range V IN = 2.5V PP at 10kHz db Isolation Channel-to-Channel db VOLTAGE REFERENCE OUTPUT Range V Internal Reference Drift ppm/ C Output Impedance Internal Reference ON Ω Internal Reference OFF 1 1 GΩ Quiescent Current Int. Ref. ON, SCL and SDA pulled HIGH µa VOLTAGE REFERENCE INPUT Range 0.05 V DD 0.05 V DD V Resistance 1 1 GΩ Current Drain High Speed Mode: SCL = 3.4MHz µa DIGITAL INPUT/OUTPUT Logic Family CMOS CMOS Logic Levels: V IH +V DD 0.7 +V DD V DD 0.7 +V DD V V IL 0.3 +V DD V DD 0.3 V V OL Min. 3mA Sink Current V Input Leakage: I IH V IH = +V DD µa I IL V IL = µa Data Format Straight Straight Binary Binary ADS7828 HARDWARE ADDRESS Binary POWER-SUPPLY REQUIREMENTS Power-Supply Voltage, +V DD Specified Performance V Quiescent Current High Speed Mode: SCL = 3.4MHz µa Fast Mode: SCL = 400kHz µa Standard Mode, SCL = 100kHz µa Power Dissipation High Speed Mode: SCL = 3.4MHz mw Fast Mode: SCL = 400kHz mw Standard Mode, SCL = 100kHz mw Power-Down Mode High Speed Mode: SCL = 3.4MHz µa w/wrong Address Selected Fast Mode: SCL = 400kHz µa Standard Mode, SCL = 100kHz µa Full Power-Down SCL Pulled HIGH, SDA Pulled HIGH na TEMPERATURE RANGE Specified Performance C NOTES: (1) LSB means Least Significant Bit. With V REF equal to 5.0V, 1LSB is 1.22mV. (2) THD measured out to the 9th-harmonic. 4 ADS7828

5 TIMING DIAGRAM SDA t BUF t LOW t R t F t HD; STA t SP SCL t HD; STA t SU; STA t SU; STO t HD; DAT t HIGH t SU; DAT STOP START REPEATED START TIMING CHARACTERISTICS (1) At T A = 40 C to +85 C, +V DD = +2.7V, unless otherwise noted. PARAMETER SYMBOL CONDITIONS MIN MAX UNITS SCL Clock Frequency f SCL Standard Mode 100 khz Fast Mode 400 khz High-Speed Mode, C B = 100pF max 3.4 MHz High-Speed Mode, C B = 400pF max 1.7 MHz Bus Free Time Between a STOP and t BUF Standard Mode 4.7 µs START Condition Fast Mode 1.3 µs Hold Time (Repeated) START t HD ; STA Standard Mode 4.0 µs Condition Fast Mode 600 ns High-Speed Mode 160 ns LOW Period of the SCL Clock t LOW Standard Mode 4.7 µs Fast Mode 1.3 µs High-Speed Mode, C B = 100pF max (2) 160 ns High-Speed Mode, C B = 400pF max (2) 320 ns HIGH Period of the SCL Clock t HIGH Standard Mode 4.0 µs Fast Mode 600 ns High-Speed Mode, C B = 100pF max (2) 60 ns High-Speed Mode, C B = 400pF max (2) 120 ns Setup Time for a Repeated START t SU ; STA Standard Mode 4.7 µs Condition Fast Mode 600 ns High-Speed Mode 160 ns Data Setup Time t SU ; DAT Standard Mode 250 ns Fast Mode 100 ns High-Speed Mode 10 ns Data Hold Time t HD ; DAT Standard Mode µs Fast Mode µs High-Speed Mode, C B = 100pF max (2) 0 (3) 70 ns High-Speed Mode, C B = 400pF max (2) 0 (3) 150 ns Rise Time of SCL Signal t RCL Standard Mode 1000 ns Fast Mode C B 300 ns High-Speed Mode, C B = 100pF max (2) ns High-Speed Mode, C B = 400pF max (2) ns Rise Time of SCL Signal After a t RCL1 Standard Mode 1000 ns Repeated START Condition and Fast Mode C B 300 ns After an Acknowledge Bit High-Speed Mode, C B = 100pF max (2) ns High-Speed Mode, C B = 400pF max (2) ns Fall Time of SCL Signal t FCL Standard Mode 300 ns Fast Mode C B 300 ns High-Speed Mode, C B = 100pF max (2) ns High-Speed Mode, C B = 400pF max (2) ns NOTES: (1) All values referred to V IHMIN and V ILMAX levels. (2) For bus line loads C B between 100pF and 400pF the timing parameters must be linearly interpolated. (3) A device must internally provide a data hold time to bridge the undefined part between V IH and V IL of the falling edge of the SCLH signal. An input circuit with a threshold as low as possible for the falling edge of the SCLH signal minimizes this hold time. ADS7828 5

6 TIMING CHARACTERISTICS (1) (Cont.) At T A = 40 C to +85 C, +V DD = +2.7V, unless otherwise noted. PARAMETER SYMBOL CONDITIONS MIN MAX UNITS Rise Time of SDA Signal t RDA Standard Mode 1000 ns Fast Mode C B 300 ns High-Speed Mode, C B = 100pF max (2) ns High-Speed Mode, C B = 400pF max (2) ns Fall Time of SDA Signal t FDA Standard Mode 300 ns Fast Mode C B 300 ns High-Speed Mode, C B = 100pF max (2) ns High-Speed Mode, C B = 400pF max (2) ns Setup Time for STOP Condition t SU ; STO Standard Mode 4.0 µs Fast Mode 600 ns High-Speed Mode 160 ns Capacitive Load for SDA and SCL C B 400 pf Line Pulse Width of Spike Suppressed t SP Fast Mode 50 ns High-Speed Mode 10 ns Noise Margin at the HIGH Level for Standard Mode Each Connected Device (Including V NH Fast Mode 0.2V DD V Hysteresis) High-Speed Mode Noise Margin at the LOW Level for Standard Mode Each Connected Device (Including V NL Fast Mode 0.1V DD V Hysteresis) High-Speed Mode NOTES: (1) All values referred to V IHMIN and V ILMAX levels. (2) For bus line loads C B between 100pF and 400pF the timing parameters must be linearly interpolated. (3) A device must internally provide a data hold time to bridge the undefined part between V IH and V IL of the falling edge of the SCLH signal. An input circuit with a threshold as low as possible for the falling edge of the SCLH signal minimizes this hold time. 6 ADS7828

7 TYPICAL CHARACTERISTICS T A = +25 C, V DD = +2.7V, V REF = External +2.5V, f SAMPLE = 50kHz, unless otherwise noted FREQUENCY SPECTRUM (4096 Point FFT: f IN = 1kHz, 0dB) 2.00 INTEGRAL LINEARITY ERROR vs CODE (2.5V Internal Reference) 1.50 Amplitude (db) ILE (LSB) Frequency (khz) Output Code 2.00 DIFFERENTIAL LINEARITY ERROR vs CODE (2.5V Internal Reference) 2.00 INTEGRAL LINEARITY ERROR vs CODE (2.5V External Reference) DLE (LSB) ILE (LSB) Output Code Output Code 2.00 DIFFERENTIAL LINEARITY ERROR vs CODE (2.5V External Reference) 1.5 CHANGE IN OFFSET vs TEMPERATURE DLE (LSB) Delta from 25 C (LSB) Output Code Temperature ( C) ADS7828 7

8 TYPICAL CHARACTERISTICS (Cont.) T A = +25 C, V DD = +2.7V, V REF = External +2.5V, f SAMPLE = 50kHz, unless otherwise noted. 1.5 CHANGE IN GAIN vs TEMPERATURE INTERNAL REFERENCE vs TEMPERATURE Delta from 25 C (LSB) Internal Reference (V) Temperature ( C) Temperature ( C) 750 POWER-DOWN SUPPLY CURRENT vs TEMPERATURE 400 SUPPLY CURRENT vs TEMPERATURE Supply Current (na) Supply Current (µa) Temperature ( C) Temperature ( C) 300 SUPPLY CURRENT vs I 2 C BUS RATE 100 INTERNAL V REF vs TURN-ON TIME Supply Current (µa) Internal V REF (%) No Cap (42µs) 12-Bit Settling 1µF Cap (1240µs) 12-Bit Settling k 10k I 2 C Bus Rate (KHz) Turn-On Time (µs) 8 ADS7828

9 THEORY OF OPERATION The ADS7828 is a classic Successive Approximation Register (SAR) A/D converter. The architecture is based on capacitive redistribution which inherently includes a sampleand-hold function. The converter is fabricated on a 0.6µ CMOS process. The ADS7828 core is controlled by an internally generated free-running clock. When the ADS7828 is not performing conversions or being addressed, it keeps the A/D converter core powered off, and the internal clock does not operate. The simplified diagram of input and output for the ADS7828 is shown in Figure 1. ANALOG INPUT When the converter enters the hold mode, the voltage on the selected CHx pin is captured on the internal capacitor array. The input current on the analog inputs depends on the conversion rate of the device. During the sample period, the source must charge the internal sampling capacitor (typically 25pF). After the capacitor has been fully charged, there is no further input current. The amount of charge transfer from the analog source to the converter is a function of conversion rate. REFERENCE The ADS7828 can operate with an internal 2.5V reference or an external reference. If a +5V supply is used, an external +5V reference is required in order to provide full dynamic range for a 0V to +V DD analog input. This external reference can be as low as 50mV. When using a +2.7V supply, the internal +2.5V reference will provide full dynamic range for a 0V to +V DD analog input. As the reference voltage is reduced, the analog voltage weight of each digital output code is reduced. This is often referred to as the LSB (least significant bit) size and is equal to the reference voltage divided by This means that any offset or gain error inherent in the A/D converter will appear to increase, in terms of LSB size, as the reference voltage is reduced. The noise inherent in the converter will also appear to increase with lower LSB size. With a 2.5V reference, the internal noise of the converter typically contributes only 0.32LSB peak-topeak of potential error to the output code. When the external reference is 50mV, the potential error contribution from the internal noise will be 50 times larger 16LSBs. The errors due to the internal noise are Gaussian in nature and can be reduced by averaging consecutive conversion results. DIGITAL INTERFACE The ADS7828 supports the I 2 C serial bus and data transmission protocol, in all three defined modes: standard, fast, and high-speed. A device that sends data onto the bus is defined as a transmitter, and a device receiving data as a receiver. The device that controls the message is called a master. The devices that are controlled by the master are slaves. The bus must be controlled by a master device that generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions. The ADS7828 operates as a slave on the I 2 C bus. Connections to the bus are made via the open-drain I/O lines SDA and SCL. +2.7V to +3.6V 5Ω + 1µF to 10µF 0.1µF REF IN / REF OUT V DD + 1µF to 10µF 2kΩ 2kΩ CH0 SDA CH1 SCL CH2 ADS7828 A0 CH3 A1 CH4 GND CH5 CH6 CH7 COM Microcontroller FIGURE 1. Simplified I/O of the ADS7828. ADS7828 9

10 The following bus protocol has been defined (as shown in Figure 2): Data transfer may be initiated only when the bus is not busy. During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in the data line while the clock line is HIGH will be interpreted as control signals. Accordingly, the following bus conditions have been defined: Bus Not Busy: Both data and clock lines remain HIGH. Start Data Transfer: A change in the state of the data line, from HIGH to LOW, while the clock is HIGH, defines a START condition. Stop Data Transfer: A change in the state of the data line, from LOW to HIGH, while the clock line is HIGH, defines the STOP condition. Data Valid: The state of the data line represents valid data, when, after a START condition, the data line is stable for the duration of the HIGH period of the clock signal. There is one clock pulse per bit of data. Each data transfer is initiated with a START condition and terminated with a STOP condition. The number of data bytes transferred between START and STOP conditions is not limited and is determined by the master device. The information is transferred byte-wise and each receiver acknowledges with a ninth-bit. Within the I 2 C bus specifications a standard mode (100kHz clock rate), a fast mode (400kHz clock rate), and a highspeed mode (3.4MHz clock rate) are defined. The ADS7828 works in all three modes. Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the reception of each byte. The master device must generate an extra clock pulse that is associated with this acknowledge bit. A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a way that the SDA line is stable LOW during the HIGH period of the acknowledge clock pulse. Of course, setup and hold times must be taken into account. A master must signal an end of data to the slave by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this case, the slave must leave the data line HIGH to enable the master to generate the STOP condition. Figure 2 details how data transfer is accomplished on the I 2 C bus. Depending upon the state of the R/W bit, two types of data transfer are possible: 1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the master is the slave address. Next follows a number of data bytes. The slave returns an acknowledge bit after the slave address and each received byte. 2. Data transfer from a slave transmitter to a master receiver. The first byte, the slave address, is transmitted by the master. The slave then returns an acknowledge bit. Next, a number of data bytes are transmitted by the slave to the master. The master returns an acknowledge bit after all received bytes other than the last byte. At the end of the last received byte, a not-acknowledge is returned. The master device generates all of the serial clock pulses and the START and STOP conditions. A transfer is ended with a STOP condition or a repeated START condition. Since a repeated START condition is also the beginning of the next serial transfer, the bus will not be released. The ADS7828 may operate in the following two modes: Slave Receiver Mode: Serial data and clock are received through SDA and SCL. After each byte is received, an acknowledge bit is transmitted. START and STOP conditions are recognized as the beginning and end of a serial transfer. Address recognition is performed by hardware after reception of the slave address and direction bit. Slave Transmitter Mode: The first byte (the slave address) is received and handled as in the slave receiver mode. However, in this mode the direction bit will indicate that the transfer direction is reversed. Serial data is transmitted on SDA by the ADS7828 while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer. SDA MSB Slave Address R/W Direction Bit Acknowledgement Signal from Receiver Acknowledgement Signal from Receiver SCL ACK ACK START Condition Repeated If More Bytes Are Transferred STOP Condition or Repeated START Condition FIGURE 2. Basic Operation of the ADS ADS7828

11 ADDRESS BYTE MSB LSB A1 A0 R/W COMMAND BYTE MSB LSB SD C2 C1 C0 PD1 PD0 X X The address byte is the first byte received following the START condition from the master device. The first five bits (MSBs) of the slave address are factory pre-set to The next two bits of the address byte are the device select bits, A1 and A0. Input pins (A1-A0) on the ADS7828 determine these two bits of the device address for a particular ADS7828. A maximum of four devices with the same pre-set code can therefore be connected on the same bus at one time. The A1-A0 Address Inputs can be connected to V DD or digital ground. The device address is set by the state of these pins upon power-up of the ADS7828. The last bit of the address byte (R/W) defines the operation to be performed. When set to a 1 a read operation is selected; when set to a 0 a write operation is selected. Following the START condition the ADS7828 monitors the SDA bus, checking the device type identifier being transmitted. Upon receiving the code, the appropriate device select bits, and the R/W bit, the slave device outputs an acknowledge signal on the SDA line. The ADS7828 operating mode is determined by a command byte which is illustrated above. SD: Single-Ended/Differential Inputs 0: Differential Inputs 1: Single-Ended Inputs C2 - C0: Channel Selections PD1-0: Power-Down Selection X: Unused See Table I for a power-down selection summary. See Table II for a channel selection control summary. PD1 PD0 DESCRIPTION 0 0 Power Down Between A/D Converter Conversions 0 1 Internal Reference OFF and A/D Converter ON 1 0 Internal Reference ON and A/D Converter OFF 1 1 Internal Reference ON and A/D Converter ON TABLE I. Power-Down Selection CHANNEL SELECTION CONTROL SD C2 C1 C0 CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM IN IN IN IN IN IN IN IN IN +IN IN +IN IN +IN IN +IN IN IN IN IN IN IN IN IN IN IN IN IN IN IN IN IN TABLE II. Channel Selection Control Addressed by Command Byte. ADS

12 INITIATING CONVERSION Provided the master has write-addressed it, the ADS7828 turns on the A/D converter s section and begins conversions when it receives BIT 4 of the command byte shown in the Command Byte. If the command byte is correct, the ADS7828 will return an ACK condition. READING DATA Data can be read from the ADS7828 by read-addressing the part (LSB of address byte set to 1) and receiving the transmitted bytes. Converted data can only be read from the ADS7828 once a conversion has been initiated as described in the preceding section. Each 12-bit data word is returned in two bytes, as shown below, where D11 is the MSB of the data word, and D0 is the LSB. Byte 0 is sent first, followed by Byte 1. MSB LSB BYTE D11 D10 D9 D8 BYTE 1 D7 D6 D5 D4 D3 D2 D1 D0 READING IN F/S MODE Figure 3 describes the interaction between the master and the slave ADS7828 in Fast or Standard (F/S) mode. At the end of reading conversion data the ADS7828 can be issued a repeated START condition by the master to secure bus operation for subsequent conversions of the A/D converter. This would be the most efficient way to perform continuous conversions. ADC Power-Down Mode ADC Sampling Mode S A 1 A 0 W A SD C 2 C 1 C 0 PD 1 PD 0 X X A Write-Addressing Byte Command Byte ADC Converting Mode ADC Power-Down Mode (depending on power-down selection bits) Sr A 1 A 0 R A D 11 D 10 D 9 D 8 A D 7 D 6...D 1 D 0 N P Read-Addressing Byte 2 x (8 Bits + ack/not-ack) See Note (1) From Master to Slave From Slave to Master A = acknowledge (SDA LOW) N = not acknowledge (SDA HIGH) S = START Condition P = STOP Condition Sr = repeated START condition W = '0' (WRITE) R = '1' (READ) NOTE: (1) To secure bus operation and loop back to the stage of write-addressing for next conversion, use repeated START. FIGURE 3. Typical Read Sequence in F/S Mode. 12 ADS7828

13 READING IN HS MODE High Speed (HS) mode is fast enough that codes can be read out one at a time. In HS mode, there is not enough time for a single conversion to complete between the reception of a repeated START condition and the read-addressing byte, so the ADS7828 stretches the clock after the read-addressing byte has been fully received, holding it LOW until the conversion is complete. See Figure 4 for a typical read sequence for HS mode. Included in the read sequence is the shift from F/S to HS modes. It may be desirable to remain in HS mode after reading a conversion; to do this, issue a repeated START instead of a STOP at the end of the read sequence, since a STOP causes the part to return to F/S mode. F/S Mode S X X X N HS Mode Master Code HS Mode Enabled ADC Power-Down Mode ADC Sampling Mode Sr A 1 A 0 W A SD C 2 C 1 C 0 PD 1 PD 0 X X A Write-Addressing Byte Command Byte HS Mode Enabled ADC Converting Mode Sr A 1 A 0 R A SCLH (2) is stretched LOW waiting for data conversion Read-Addressing Byte HS Mode Enabled Return to F/S Mode (1) ADC Power-Down Mode (depending on power-down selection bits) D 11 D 10 D 9 D 8 A D 7 D 6...D 1 D 0 N P 2 x (8 Bits + ack/not-ack) From Master to Slave From Slave to Master A = acknowledge (SDA LOW) N = not acknowledge (SDA HIGH) S = START Condition P = STOP Condition Sr = repeated START condition W = '0' (WRITE) R = '1' (READ) NOTES: (1) To remain in HS mode, use repeated START instead of STOP. (2) SCLH is SCL in HS mode. FIGURE 4. Typical Read Sequence in HS Mode. ADS

14 READING WITH REFERENCE ON/OFF The internal reference defaults to off when the ADS7828 power is on. To turn the internal reference on or off, see Table I. If the reference (internal or external) is constantly turned on and off, a proper amount of settling time must be added before a normal conversion cycle can be started. The exact amount of settling time needed varies depending on the configuration. See Figure 5 for an example of the proper internal reference turn-on sequence before issuing the typical read sequences required for the F/S mode when an internal reference is used. When using an internal reference, there are three things that must be done: 1) In order to use the internal reference, the PD1 bit of Command Byte must always be set to logic 1 for each sample conversion that is issued by the sequence, as shown in Figure 3. 2) In order to achieve 12-bit accuracy conversion when using the internal reference, the internal reference settling time must be considered, as shown in the Internal V REF vs Turn-On Time Typical Characteristic plot. If the PD1 bit has been set to logic 0 while using the ADS7828, then the settling time must be reconsidered after PD1 is set to logic 1. In other words, whenever the internal reference is turned on after it has been turned off, the settling time must be long enough to get 12-bit accuracy conversion. 3) When the internal reference is off, it is not turned on until both the first Command Byte with PD1 = 1 is sent and then a STOP condition or repeated START condition is issued. (The actual turn-on time occurs once the STOP or repeated START condition is issued.) Any Command Byte with PD1 = 1 issued after the internal reference is turned on serves only to keep the internal reference on. Otherwise, the internal reference would be turned off by any Command Byte with PD1 = 0. The example in Figure 5 can be generalized for a HS mode conversion cycle by simply swapping the timing of the conversion cycle. If using an external reference, PD1 must be set to 0, and the external reference must be settled. The typical sequence in Figure 3 or Figure 4 can then be used. Internal Reference Turn-On Sequence S A 1 A 0 W A X X X X 1 X X X A P Internal Reference Turn-On Settling Time Wait until the required settling time is reached Write-Addressing Byte Command Byte ADC Power-Down Mode Settled Internal Reference ADC Sampling Mode Typical Read Sequence (1) in F/S Mode S A 1 A 0 W A SD C 2 C 1 C 0 1 PD 0 X X A Write-Addressing Byte Command Byte Settled Internal Reference ADC Converting Mode ADC Power-Down Mode (depending on power-down selection bits) Sr A 1 A 0 R A D 11 D 10 D 9 D 8 A D 7 D 6...D 1 D 0 N P Read-Addressing Byte 2 x (8 Bits + ack/not-ack) see note (2) From Master to Slave From Slave to Master A = acknowledge (SDA LOW) N = not acknowledge (SDA HIGH) S = START Condition P = STOP Condition Sr = repeated START condition W = '0' (WRITE) R = '1' (READ) NOTES: (1) Typical read sequences can be reused after the internal reference is settled. (2) To secure bus operation and loop back to the stage of write-addressing for next conversion, use repeated START. FIGURE 5. Internal Reference Turn-On Sequence and Typical Read Sequence (F/S mode shown). 14 ADS7828

15 LAYOUT For optimum performance, care should be taken with the physical layout of the ADS7828 circuitry. The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground connections, and digital inputs that occur just prior to latching the output of the analog comparator. Therefore, during any single conversion for an n-bit SAR converter, there are n windows in which large external transient voltages can easily affect the conversion result. Such glitches might originate from switching power supplies, nearby digital logic, and high-power devices. With this in mind, power to the ADS7828 should be clean and well-bypassed. A 0.1µF ceramic bypass capacitor should be placed as close to the device as possible. A 1µF to 10µF capacitor may also be needed if the impedance of the connection between +V DD and the power supply is high. The ADS7828 architecture offers no inherent rejection of noise or voltage variation in regards to using an external reference input. This is of particular concern when the reference input is tied to the power supply. Any noise and ripple from the supply will appear directly in the digital results. While high-frequency noise can be filtered out, voltage variation due to line frequency (50Hz or 60Hz) can be difficult to remove. The GND pin should be connected to a clean ground point. In many cases, this will be the analog ground. Avoid connections that are too near the grounding point of a microcontroller or digital signal processor. The ideal layout will include an analog ground plane dedicated to the converter and associated analog circuitry. ADS

16 PACKAGE OPTION ADDENDUM 28-Apr-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan ADS7828E/250 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828E/250G4 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828E/2K5 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828E/2K5G4 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828EB/250 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828EB/250G4 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828EB/2K5 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) ADS7828EB/2K5G4 ACTIVE TSSOP PW Green (RoHS & no Sb/Br) (2) Lead/Ball Finish MSL Peak Temp (3) Op Temp ( C) CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E B CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E B CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E B CU NIPDAU Level-1-260C-UNLIM -40 to 85 ADS 7828E B Top-Side Markings (4) Samples (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) Addendum-Page 1

17 PACKAGE OPTION ADDENDUM 28-Apr-2013 (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Top-Side Marking for that device. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. OTHER QUALIFIED VERSIONS OF ADS7828 : Automotive: ADS7828-Q1 NOTE: Qualified Version Definitions: Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects Addendum-Page 2

18 PACKAGE MATERIALS INFORMATION 24-Apr-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Reel Diameter (mm) Reel Width W1 (mm) A0 (mm) B0 (mm) K0 (mm) P1 (mm) W (mm) Pin1 Quadrant ADS7828E/250 TSSOP PW Q1 ADS7828E/2K5 TSSOP PW Q1 ADS7828EB/250 TSSOP PW Q1 ADS7828EB/2K5 TSSOP PW Q1 Pack Materials-Page 1

19 PACKAGE MATERIALS INFORMATION 24-Apr-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) ADS7828E/250 TSSOP PW ADS7828E/2K5 TSSOP PW ADS7828EB/250 TSSOP PW ADS7828EB/2K5 TSSOP PW Pack Materials-Page 2

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